Magnetic Shutter Mechanical Antenna for Cross-Media Communication

In low-frequency cross-media communication systems, traditional mechanical antennas have problems such as limiting the upper limit of operating frequency due to motor speed, waveform distortion, and limiting transmission rate due to modulation methods. Thus, we have designed a new magnetic shutter type mechanical antenna. It is designed based on the radiation equation of a rotating magnetic dipole, combined with the principle of relative motion between the magnetic dipole and the high permeability shutter material. Relying upon the rotation of the shutter structure, the magnetic field of the spherical permanent magnet array is intermittently shielded, generating a low-frequency magnetic induction signal that is multiplied by the motor speed. The entire antenna system uses a cross array of spherical permanent magnets with two evenly distributed magnetic poles and a two-dimensional signal modulation method that combines frequency modulation and amplitude modulation, so it has high radiation intensity and transmission rate in the ultra-low frequency band. Experimental results show that when the motor speed is $n$ r/s (rad per second), the operating frequency of the mechanical antenna can reach 4n Hz, and the signal amplitude measured at 5 m is 50 mV, which is about 3.5 nT. Compared with the current mechanical antenna of the same volume, its signal radiation intensity is stronger.